Conventionally, the decorative parts, such as a wristwatch band and other wristwatch parts, a finger ring, a necklace and an earring, have been provided with a high quality appearance and an excellent corrosion resistance by composing its outermost layer of a gold coating formed according to a wet or dry plating process. The respective outermost layers of such decorative parts are now increasingly composed of a coating of a gold alloy, such as gold-nickel and gold-palladium alloys, rather than of that of pure gold, because the pure gold coating is so soft as to have less wear resistance, and because the color of the pure gold is not favored due to its extremely deep golden tone and rather there is an inclination that light golden color is preferred.
However, in recent years, a marked increase is observed in the occurrence of allergic dermatitis in which contact dermatitis is caused by the contact of the skin with a decorative part, such as a necklace or an earring, made of a precious metal. Such allergic dermatitis cases are reported with respect to almost all types of metals. Especially, the occurrence of allergic dermatitis attributed to gold-nickel and gold-palladium alloys is described in many reports.
Titanium is a metal for which no allergic dermatitis case has been reported. However, the employment of titanium in an ion plating process to form an outermost coating of the above decorative part has been accompanied by drawbacks such that the tone of the resultant gold-titanium alloy coating is not uniform, and that the coating becomes blackish. Iron is another metal for which allergic dermatitis cases have been extremely rarely reported. However, the employment of iron in an ion plating process to form an outermost coating of the above decorative part has also been accompanied by drawbacks such that the tone of the resultant gold-iron alloy coating is not uniform, and that the coating becomes blackish. Extensive study has been made to find what causes such drawbacks. As a result, it has been found that titanium and iron are so active that large amounts of oxygen, carbon and nitrogen present in an ion plating apparatus are captured into the coating, and that the above drawbacks are caused by such capturing.
As indicated above, there has been a strong demand in the art for the development of a golden decorative part not only having no danger of causing allergic dermatitis, such as contact dermatitis, even if used in contact with the skin but also exhibiting a uniform golden tone.
The present invention has been made with a view toward obviating the above drawbacks of the prior art. Thus it an object of the present invention to provide a golden decorative part not only having no danger of causing allergic dermatitis, such as contact dermatitis, even if used in contact with the skin but also exhibiting a uniform golden tone. It is another object of the present invention to provide a process for producing the above golden decorative part.